A known type of sonobuoy incorporates acoustic sensors which are contained in a housing until such time as the sonobuoy is dropped into the water, at which time the sensors are released from the housing as an array to detect acoustic signals in the water. The sonobuoy incorporates a float from which the array is suspended by a line and which serves to pull the array out of the housing when it has descended to a depth determined by the length of the line. Fastening means may be provided to retain the array within the housing during descent, but which is released by the inertial force exerted by the housing when the line is fully extended. Once pulled out of the housing, the array may be deployed by gravity or spring means. However, deployment of the array in this way may not be sufficient to ensure fully effective deployment.
In other known types of sonobuoy, drive means is provided to positively deploy the sensor array.
For example, spring powered motors may be provided which are connected to pivoted arms carrying the sensors so that these arms are swung outwards from a tubular configuration to a star-shaped configuration when the motors are operated. However, the provision of such drive means complicates the design of the sonobuoy and increases its cost.